Thermostat replacement, 3.1

Having done this today, and remembering someone having questions about it not long ago, I thought I'd write up a quick bit in case someone seaches for these answers.

I'd done many 3.1 t-stats in the shop, but at the time, mine ('97) would have been fairly new, hadn't done one like it. So today was a learning experience for me.

I remembered that the t-stat outlet WOULD come off with the exhaust crossover in place, but there was a trick to it...the casting's bolt hole closest to the firewall is actually a notch, so you could leave that bolt in place and slide the housing towards the front of the car and off, without fully removing the bolt, which interfered with the exhaust crossover when fully backed out.

I'd seen people go nuts because they couldn't fully remove that bolt, when in reality, you don't have to. I figured and hoped this one would be the same.

Well, it is and it isn't. And as far as access to that bolt goes, it may be possible to do it with minimal dis-assembly, but you'd have to have trickier tools than I do. I had nothing I could put on it and have any leverage much less any room to swing it if I could break it loose.

I tend to do things in a "path of least resistance" manner, which on stuff like this means resigning myself to just take the extra time to remove anything that is impeding my access.

So the progression went like this:

1) Remove the airbox to intake ducts and MAF sensor. Spray the exhaust crossover shield bolts with penetrating oil NOW.
2) Remove the EGR valve and the A.I.R. pipe, and push it out of the way.
3) Remove the heater hose and two throttle plate heat hoses from the metal pipe that runs over to the water pump casting cavity.
4) Remove the hold-down nuts from this pipe and remove the bolt that holds it into the top of the cavity above the pump, remove the pipe from the motor. You'll need to remove the bypass hose and pull the front 3 plug wires off and some vacuum lines to take it all the way off.
5) Remove the airbox (one bolt on the left side of the box)
6) Remove the exhaust crossover heat shield. Pay attention to how you have to turn it to remove it, it will only go back in place the same way.

Now you have pretty clean access to the thermostat outlet and its bolts. I'll say at this point I did try to change it out with the crossover heat shield in place, but there was a maddeningly small bit of three way interference between the new thermostat, due to a slightly different from OEM shaping, the thermostat outlet, and the heat shield. I just could NOT slip the outlet back in place over the new thermostat while that rear bolt was in place.

The solution would seem to be to position the outlet, THEN put the rear bolt in place, but I assure you the shield makes this EXTREMELY difficult, if not impossible. I tried and tried to get the bolt started with the limited access, and even after grinding the bolt's end to a point to help it "find" the hole, I still could not get it started...part of the problem was the limited space available was forcing my hands to push downward on the outlet, making starting the bolt impossible.

But once the shield was removed, it opened up just enough room to make things (comparatively) easy. Putting the outlet and its bolts back in place was pretty straightforward now, with just enough room to allow my fingers to do what they needed to do.

With that taken care of, finishing the job was simply a matter of replacing all the above items, in the reverse order that they were removed. And finally, of course, properly bleeding the system while refilling.

Like I said, I have certain limitations created by the tools I have available, and the size and shape of my fingers and hands....I could see where a person with smaller hands or better tools MIGHT be able to complete this job without removing so much stuff, but I figure you might as well know what's probably gonna be required, and if you can snake outta some of it, good on you.

I welcome any comments or criticism, if I totally missed something that might have made this simpler, I'd love to hear it, and have it documented for the person who turns up this thread while searching for advice with this job.

I was just glad to have not had to remove the crossover pipe...I don't like messing with 13 year old exhaust flange bolts, for obvious reasons.

EDIT: I forgot to mention that early on in the process, I did unbolt the dogbones (torque struts) and roll the motor forward, I thought it would help my access to the rear crossover flange if it became necessary to remove it. It did help access to the rear shield bolts as well though, but might not have been necessary, in hindsight.

Nice tutorial. I know it will help those who find it.

Nice tutorial. I know it will help those who find it.

Thanks!

I forgot....I also meant to use this as yet another example to make the case for keeping your motor clean...I wash mine at least twice a year, spring and fall, sometimes a couple of times during the winter.

It's amazing the difference it makes, both in the condition of the various parts, and the comfort level of working on it....

My wiring, hoses, lines, etc are all still in great shape, not brittle and easy to crack like most this age. My OE plug wires still feel like new, they unplug easily and the boots are not swollen or oily and are easy to grab and pull off. Usually, most cars this age, they are puffed up from oil/chemical rot, and stuck on the plugs so bad you have to grab them with a puller, and half the time the terminals separate when you try to pull them off. Mine still have that nice solid positive feel of a new set.

That heater hose pipe should be shucking all its paint and corroded to hell by now, and possibly even crack and leak after being removed from the engine, as was the case often in the shop...usually we'd advise it would have to be replaced if it fell apart while being removed, which they often did.

Mine looks perfect....solid paint all around, I could have wiped it off and hand it to you and you'd think it was a new part. I was particularly surprised by that.

Those exhaust shield bolts were rusty, no getting around that, but they still have their shape, fit the socket, and came apart very easily....and I noticed that even though as I said I was glad I didn't have to remove the crossover pipe, the flange bolts appeared to be in excellent shape....minimally rusty and good threads visible, I think they would have come apart without any major trauma....

And the best part....working in close quarters, your hands stay cleaner, which is important when you're trying to manipulate tools and small hardware in tight spaces....makes things SO much less aggravating when you can actually hold onto things and see clearly what you're looking at....not trying to find bolts and nuts hidden under layers of crud, etc...

It's really well worth the slight expense and time it takes to do a few times a year. The payback is priceless when the time comes...:wink: